
/*回到顶部*/
#btn {
    display: none;
    position: fixed;
    right: 2%;
    bottom: 14%;
    width: 50px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    /*自上而下渐变色*/
    /*background: -webkit-linear-gradient(top, #000, red, yellow, blue);*/
    background-color: rgba(229, 228, 222, 0.5);
    border-radius: 35%;
    opacity: 0.5;
    filter: alpha(opacity=50);
}

#btn:hover {
    opacity: 1;
    filter: alpha(opacity=100);
    /*透明度兼容*/
}
